Notification test reworked
Removed __del__ method from Card and Sector classes

Reader class changed to support context management.
Handler metaclass improved.

+ required and default arguments are now being checked correctly via Args
  class.
+ 'reader' request parameter should now only be mapped to Reader instance
  if method being called requires it.
+ api_callback now uses Reader context management properties.
test_interface now correctly calls `close` on reader intstances.
Notification behaviour around reader changed according to new context management.
Reader detection mechanics should now work correctly in threading model.

+ conttextlb.closing utilized during reader identification process.
+ reader closing procedure should now be thread-safe